Galvanic Cells

The reactions most commonly involved in electrochemistry are oxidation-reduction reactions, which involve a transfer of electrons from the reducing agent to the oxidizing agent.  The key to harnessing the chemical energy that comes from these reactions is separating the oxidizing agent from the reducing agent, which requires the electron transfer to occur through a wire.  The current produced in the wire by the electron flow from the redox reactions can then be directed into a device such as a motor to provide work.
However, sometimes the current stops flowing because of charge buildups in the two compartments of an apparatus.  The solutions then must be connected so that ions can flow to keep the net charge in each compartment zero.  A salt bridge or a porous disk is required to allow ions to flow without extensive mixing of the solutions.
The electrode compartment in which oxidation occurs is called the anode and the electrode compartment in which reduction occurs is called the cathode.
These are the characteristics of a galvanic cell, which is defined as a device in which chemical energy is changed to electrical energy.
Cell potential (unit=volt) is the driving force on the electrons that occurs when the oxidizing agent in one compartment of the cell pulls electrons through a wire from the reducing agent.  Cell potential can be measured by a voltmeter or a more accurate potentiometer.  Potentiometers are better at representing maximum cell potential, in which no energy is wasted.